A bright blue flash lit up the sky over Spain and Portugal

Why was it such a strange color?

The color of a meteor depends on its chemical composition and how fast it passes through the atmosphere. For example, yellow meteors are usually formed by the combustion of sodium-rich motheoroid, orange-yellow indicates the presence of iron, blue-green indicates magnesium, purple indicates calcium, and red meteors are formed by the heating of nitrogen and oxygen in the atmosphere.